The invention relates to a wobble motor for linear and/or rotary movements.
Electromagnetic motors are known in which a rotary movement is converted into a linear movement by a gear worm.
The references by M. Bexell, S. Johansson, titled xe2x80x9cFabrication and Evaluation of a Piezoelectric Miniature Motorxe2x80x9d, Sensors and Actuators 75 (1999) p. 8-16, and M. Bexell, S. Johansson, titled xe2x80x9cCharacteristics of a Piezoelectric Miniature Motorxe2x80x9d, Sensors and Actuators 75 (1999) p. 118-130, disclose a miniaturized, xe2x80x9cinchworm motorxe2x80x9d in which a rotation is effected by contraction and bending of a plurality of piezoelectric elements.
A reference by G. Schadebrodt and B. Salomon, titled xe2x80x9cThe Piezo Traveling Wave Motor, a New Element in Actuationxe2x80x9d, PCIM, July 1990, describes a traveling wave motor in which a stator uses the piezeoelectric effect to generate a resonant wave motion on its surface, and thus drives a rotor.
A further piezoelectrically driven traveling wave motor is described in European Patent EP 0 788 664 B1.
A reference by M. Fleischer, H. Meixner, titled Ultraschallmotoren mit piezoelektrischem Antrieb [Ultrasonic Motors With Piezoelectric Drive], Physik in unserer Zeit, 22nd annual volume 1991, No. 4, discloses an ultrasonic motor with a piezoelectric drive in the case of which rods excited piezoelectrically in the ultrasonic region drive a cylindrical rotor by asymmetric mounting.
An overview of piezoceramic drives is given in the reference by H. Anger, titled Piezoelektrische Vibroantriebexe2x80x94eine xc3x9cbersicht xc3xcber wesentliche technische Lxc3x6sungen [Piezoelectric Vibratory Drivesxe2x80x94An Overview Of Essential Technical Solutions], Hermsdorfer technische Mitteilungen, 30th annual volume, June 1990, volume 78, pages 2481 to 2485.
Published, Non-Prosecuted German Patent Application DE 27 09 006 A1 discloses a conversion of a rotary movement into a feed movement of a shaft by a plurality of tilted rolling members, the rolling members being driven to rotate about an axis.
It is accordingly an object of the invention to provide a Wobble motor which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, which is of light-construction and efficient, in particular for generating a high torque in conjunction with a low rotational speed without an additional transmission.
With the foregoing and other objects in view there is provided, in accordance with the invention, a wobble motor. The wobble motor contains at least one shaft guided in a rotatably and axially displaceable fashion. At least one drive ring surrounds the shaft and is tilted with respect to a longitudinal axis of the shaft. The at least one drive ring is displaced about the shaft in a frictionally locked fashion and free from rotation.
The wobble motor has at least one shaft guided in a rotably and axially displaceable fashion. Furthermore, at least one drive ring is present which surrounds the shaft. The shaft can be guided, for example, via a bearing or without a bearing by a plurality of drive rings.
The at least one drive ring can, moreover, be tilted with respect to a longitudinal axis of the shaft. It can be displaced about the shaft in a frictionally locked fashion and at least partly free from rotation.
The displacement movement can be periodic, for example circular or elliptical. Of course, only segments of such movements can also be executed.
xe2x80x9cFree from rotationxe2x80x9d is taken to mean that the drive ring can be displaced or driven as a whole around the shaft, but at least a part of the drive ring is not substantially rotated about an axis fixed in the body. It is possible in this case for the non-rotating part of the drive ring, for example an outer annular shell, to be freely rotatable against another part, for example an inner annular shell. The displacement of the drive ring therefore takes place in a fashion free from rotation.
The frictional lock between the drive ring and shaft ensures that the movement of the drive ring is transmitted to the shaft. This does not exclude the possibility of freewheeling by canceling the frictional locking.
The tilting effects a relative inclination of the drive ring in the direction of the longitudinal axis of the shaft. The tilting can be expressed as a rule by a tilting angle, which can be constant or variable in time.
It may be assumed for the purpose of better understanding in the following description that the longitudinal axis of the shaft is situated on the z-axis, and that the drive ring is disc-shaped. In the case of a tilting angle d=0 (xe2x80x9crest positionxe2x80x9d), the drive ring may be aligned with a plane (xe2x80x9cring planexe2x80x9d) which corresponds to the (x, y)-plane. However, the wobble motor is not, of course, limited to this configuration, but can also have, for example, other tilted positions or differently formed drive rings.
The wobble motor can be driven in the operating modes of pure linear drive, pure rotary drive or a combination of these two types of operation.
A plurality of drive rings can be moved independently of one another or in a fashion coupled to one another.
The wobble motor has the advantage that it is of low wear, since only rolling friction occurs. Furthermore, only a slight noise is developed. There is also the advantage that a high drive torque can be transmitted. Again, to its advantage the wobble motor can be controlled universally, for example in stepwise or continuous fashion with respect to its direction of rotation and feed direction, its rotational speed and feed rate, and its torque and feed momentum. In addition, the rotary movement and linear feed can be implemented separately or in combination. Self locking or freewheeling can also be controlled.
Furthermore, a low structural weight results in conjunction with a compact configuration, inter alia because no transmission is required.
It is also possible to achieve a favorable high efficiency. Short run up and stopping times in the millisecond range can likewise be realized.
The drive ring of the wobble motor is tilted with respect to the shaft by at least one tilting device having at least one actuator. It is advantageous when the tilting device contains at least two linear actuators. Two drive rings can be tilted by in each case one tilting device having in each case two linear actuators, or by a common tilting device having two actuators. A comparatively simple control of the tilting movement, for example by overlapping of linear movements, is possible through the use of at least two linear actuators.
It is particularly advantageous when the preferably linear actuators of the tilting device are aligned substantially parallel to the longitudinal axis of the machine, because this results in a further simplified control of the tilting movement.
It is also advantageous for the purpose of simple control of the tilting movement when the actuators of the tilting device are fitted in an angularly symmetrical fashion and at the same distance with reference to the center of the drive ring.
Advantageous for the purpose of simple control is a tilting device having three actuators, in particular fitted in an annularly symmetrical fashion and at the same distance with reference to the center of the drive ring.
It is also favorable when the at least one drive ring can be displaced about the shaft by at least one drive device containing at least two actuators which are not collinearly aligned. It is thereby possible in a simple way to execute any desired movement in a plane. Simple movement in a plane is ensured particularly in the case of a configuration of the actuators of the respective drive device perpendicular to the longitudinal axis and at right angles to one another.
Drive devices and tilting devices can also be coupled permanently, for example mechanically, and be moved by common actuators.
It is favorable when at least one actuator, in particular all the actuators, is an electromechanical actuator. In the case of an electromechanical actuator, a change in volume, and thereby a stroke, can be implemented by an electric control variable, for example a current or a voltage. One example of an electromechanical actuator is a piezoelectric, magnetostrictive or electrostrictive actuator. Such an actuator has the advantage that it can be driven very quickly and precisely.
A piezoelectric multilayer actuator in particular is cost-effective, can be produced at high precision and can be moved precisely.
It can be advantageous to use a hydraulic or electromagnetic actuator in order to achieve a cost-effective wobble motor.
It is particularly advantageous when the wobble motor has at least one further drive ring at least parallel to a first drive ring. The torque of the shaft can thereby be increased.
It is particularly advantageous in this case when the two drive rings are supported against one another by at least one tilting device, because this results in a space-saving and cost-effective configuration. However, such a positioning of the drive rings and tilting device is not mandatory.
It is also advantageous when the wobble motor has at least a third drive ring which is parallel to the first and to the further drive ring. This renders it possible to operate the shaft in a fashion free from torque and without a separate bearing. In this case, the shaft can be guided exclusively by the drive rings themselves.
It is particularly advantageous in this case when the further (middle) drive ring is supported both against the first drive ring and against the third drive ring with the aid of a tilting device in each case, because this results in a space-saving and cost-effective configuration. However, such a positioning of the drive rings and tilting device is not mandatory.
In accordance with an added feature of the invention, a respective contact point of the first drive ring and the second drive ring with the shaft is rotated by 180xc2x0 about the longitudinal axis.
In accordance with another feature of the invention, the shaft is guided through the first drive ring, the second drive ring and the third drive ring without torques.
In accordance with an additional feature of the invention, at least one bearing is provided and the shaft is guided through the at least one bearing.
In accordance with a further feature of the invention, the drive ring has a freely rotatable inner annular shell bearing against the shaft.
It can be advantageous for the purpose of improved guidance, in particular when there are less than three drive rings or an configuration of three or more drive rings which is not free from torque, if the shaft is guided through at least one bearing, in particular two bearings. The selection of the bearing is not limited, but permits an axial movement and a rotary movement of the shaft therein, for example in the form of sliding or rolling bearings. In this case, a position of the shaft that is characterized thus only partially is sufficient.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for driving a shaft. The method includes the steps of displacing at least one drive ring in an at least partially periodic movement about the shaft in a frictionally locked fashion free from rotation; and titling the at least one drive ring with respect to a longitudinal axis of the shaft.
In accordance with an added mode of the invention, there is the step of displacing the at least one drive ring perpendicularly about the longitudinal axis of the shaft at least temporarily in accordance with one of:
x=xe2x88x92(Rxe2x88x92r)xc2x7cos(xcfx89t)y=(Rxe2x88x92r)xc2x7sin(xcfx89t),
and
x=xe2x88x92(Rxe2x88x92r)xc2x7cos(xcfx89t)y=xe2x88x92(Rxe2x88x92r)xc2x7sin(xcfx89t),
where:
r is a radius of the shaft; and
R is a radius of the at least one drive ring.
It is favorable for uniform operation when the drive ring is displaced at least partially periodically, in particular circularly, in a plane in a perpendicular fashion about the longitudinal axis on the shaft. Because of the stiffness of the drive ring, each point on the drive ring executes the same movement.
It is advantageous for the production of the uniform linear movement of the shaft when the drive ring is also periodically tilted.
It is particularly favorable when the drive ring is tilted periodically at an angular frequency hat corresponds to an angle of frequency of a periodic displacement of the drive ring, if appropriate displaced by a phase angle.
The shaft can be set simply and with a constant speed, in particular by tilting the drive ring by selecting a phase angle in the range [0;xcfx80].
It is favorable for the purpose of simple driving using a small angle approximation when a tilting angle is less than 2xc2x0, in particular less than 0.1xc2x0.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a Wobble motor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.